An Adaptive Code and Modulation (ACM) technology is a transmission technology having a channel adaptive characteristic. According to the ACM technology that is based on channel estimation, an available condition of an air interface link is estimated in real time through a detecting mechanism of a receiving end, a switching indication for a coding manner and a modulation mode is automatically generated and then fed back to a transmitting end through a feedback channel, and the transmitting end automatically changes the modulation mode and the coding manner of services according to the switching indication, so as to reach a compromise between system capacity and system anti-interference ability, thus optimizing whole transmission performance of the system, and achieving highly-efficient and reliable transmission. With the development of the microwave communication technology, a further requirement is set for the performance of a microwave communication system. The existing microwave communication system must have abilities of changing and adjusting in real time the coding manner and the modulation mode of the system according to the channel quality, that is to say, an ACM function becomes one of the indispensable functions in the microwave communication system.
In a microwave device, since quality of an air interface fluctuates dramatically over time, in order to ensure reliable transmission of user services, the microwave device protects the user services by adopting a Hitless Switch Mode (HSM) protection manner. The HSM function mainly completes service protection at sides of wave channels, and is one of the essential functions of conventional microwave devices. In the HSM protection manner, services of the same link are transmitted through two different wave channels, and the receiving end compares quality of services received through the two channels and selects a service with better quality.
With the rapid development of the microwave communication technology, the ACM function becomes more and more important while the HSM function is one of the essential functions of traditional microwave devices. The HSM function realizes service protection, the ACM function realizes link protection, and the ACM function combined with the HSM function can effectively improve transmission efficiency and transmission reliability of the microwave system. Therefore, how to realize coordinated operation between the ACM and the HSM in the microwave communication system becomes a problem that needs to be solved.
Referring to a schematic view of principle as shown in FIG. 1, in the conventional art, a device transmits services of the same path through a Hot Standby (HSB) service dual transmitting unit to an active link and a standby link for transmission. During the transmission, an ACM unit of the standby link remains Off all the time, and an ACM unit of the active link remains “On.” The ACM unit of the active link performs ACM switching according to signal quality of the active link, and transmits the service after ACM switching to the standby link through the service dual transmitting unit of ACM switching, and the standby link follows the active link to perform ACM switching and maintains consistency with the active link, so as to guarantee bandwidth consistency of master and slave services. An HSM unit of the receiving end only performs HSM switching according to a code-uncorrectable signal of the active/standby link. After HSM switching, the active and standby links still perform ACM switching according to the signal quality of the active link.
In the implementation of the coordinated operation between the ACM and the HSM, the inventor finds that the conventional art has at least the following problems. If the active link keeps degrading while the standby link has better signal quality, the ACM of the active link continues to be switched downward, and the standby link has to follow the active link to be switched downward, so capacity of the air interface decreases. As shown in FIG. 1, the active link has bad signal quality and can only transmit 2M services, and the standby link has good signal quality and can transmit 8M services; but as the standby link and the active link are interlinked, the standby link can only transmit 2M services. If the signal quality of the active link is not restored, both the active and standby links operate in a low-modulation mode, and the capacity of the air interface cannot be restored. In the process of ACM switching, if the services of both links have no burst error code, the HSM can only operate when being switched to a minimum modulation mode. Therefore, the system has lower transmission efficiency. Moreover, if the active link keeps being optimized while the standby link has bad signal quality, the modulation mode of the active and standby links continue to be switched upward, and the standby link may be interrupted. At this time, if a transient error code occurs in the active link, an error occurs in HSM switching, resulting in poor reliability.